Unlike analog television where received radio waves are demodulated for display, digital moving image signals are typically reproduced with a delay between the reception of the coded data and the reproduction of the same.
With moving image coding methods defined in MPEG (Moving Picture Experts Group) and the like, the amount of code to be generated varies greatly from one frame to another. In a viewing environment of limited bandwidth, there can occur fluctuations in the reception time of the frame data.
Bi-directional prediction encodes frames in changed order, which means that some of the frames will be received with a delay. If contents only demanded by a viewer are transmitted on an on-demand basis, there occurs a transmission delay from the viewer's view request to the reception of the data.
For the sake of reproducing contents immediately after a reproduction request or reproducing a plurality of pieces of contents without interruption, a technology called caching has been used to read the first data of the contents in advance.
As a concrete example of caching, a moving image distribution system with a read-ahead function described in PTL 1 will be described. FIG. 8 is a block diagram showing the configuration of the moving image distribution system with a read-ahead function described in PTL 1.
The technology described in PTL 1 includes a transmitting unit 910 that transmits content data and a receiving unit 920 that receives and reproduces the content data.
The transmitting unit 910 includes a transmission data storing unit 100, a first data transmitting unit 98, and a subsequent data transmitting unit 99. The receiving unit 920 includes a reception data storing unit 199 and a reproducing unit 201.
Next, description will be given of the operation of the technology described in PTL 1.
Initially, the first data transmitting unit 98 transmits first data 1002 of content data stored in the transmission data storing unit 100 as long as a first data reproduction time 1100 to the receiving unit 920.
The receiving unit 920 stores the transmitted first data 1002 into the reception data storing unit 199. When the receiving unit 920 reproduces the contents, the reproducing unit 201 reproduces the first data 1004 stored in the reception data storing unit 199.
In the meantime, the subsequent data transmitting unit 99 transmits subsequent data 1003, which is the data on the contents subsequent to the duration of the first data reproduction time 1100, to the receiving unit 920. The reproducing unit 201 reproduces the subsequent data 1003 subsequently to the reproduction of the first data 1004.